Amastin mRNA abundance in Trypanosoma cruzi is controlled by a 3 '-untranslated region position-dependent cis-element and an untranslated region-binding protein

The genome of Trypanosoma cruzi contains tandem arrays of alternating genes encoding amastin and tuzin. Amastin is a surface glycoprotein abundantly e xpressed on the intracellular mammalian amastigote form of the protozoan pa rasite, and tuzin is a G-like protein. We demonstrated previously that the amastin-tuzin gene cluster is polycistronically transcribed to an equal ext ent in all parasite life cycle stages. The steady state level of amastin mR NA, however, is 68-fold more abundant in amastigotes than in epimastigotes. Here we show that the half-life of amastin mRNA is 7 times longer in amast igotes than in epimastigotes. Linker replacement experiments demonstrate th at the middle one-third of the 630-nucleotide 3'-untranslated region (UTR) is responsible for the amastin mRNA up-regulation. This positive effect is dependent on the distance of the 3'-UTR segment from the stop codon and the polyadenylation site as well as on its orientation. A protein or protein c omplex more abundant in amastigotes than in epimastigotes binds to this min imally defined 3'-UTR segment and may be involved in its regulatory functio n.